In the conventional method for driving a 2-phase SRM, two position sensors are used to detect each position of a rotor, and generated sensor signals serve to initialize and drive each phase.
FIG. 1 is a view schematically showing a construction for detecting a sensor signal of a 2-phase SRM.
As shown, the 2-phase SRM comprises a 4-pole stator 10, a 2-phase rotor 11, a rotor shaft 12 connected to the center of the rotor 11 for transmitting a rotary motion of the rotor, a 2-phase shutter 13 rotatably connected to the rotor shaft 12, 1-phase and 2-phase sensors 14a and 14b for detecting a position of the shutter 13, and a sensor signal generator 15 for generating 1-phase and 2-phase sensor signals from signals detected by the 1-phase and 2-phase sensors 14a and 14b. 
Each phase of the shutter 13 has an angle of 120°, and the two phases form an angle of 60° therebetween.
The 1-phase and 2-phase sensors 14a and 14b form an angle of 90° therebetween, and are positioned on the shutter 13.
In the conventional method for driving an SRM, when the shutter 13 is rotated as the rotor 11 is rotated, the sensors 14a and 14b detect each position of each phase of the shutter 13. Then, the sensors 14a and 14b transmit the detected position to the sensor signal generator 15 thus to enable 1-phase and 2-phase sensor signals to be generated.
That is, the 1-phase and 2-phase sensors respectively detect each position of each phase of the rotor, and then a microprocessor (not shown) generates 1-phase and 2-phase signals corresponding to the sensor signals. Accordingly, a current is supplied to each winding of each phase of the SRM thus to generate a torque.
FIGS. 2 to 5 show sensor signals according to each position of a rotor of the 2-phase SRM in accordance with the conventional art.
As shown, when the rotor 11 is counterclockwise rotated, the shutter 13 connected to the rotor shaft 12 starts to be rotated. The 1-phase and 2-phase sensors 14a and 14b detect a position of the shutter 13 thus to detect a position of the rotor 11. Accordingly, the sensor signal generator 15 generates a sensor signal of each phase.
Referring to FIGS. 2 to 5, when the rotor 11 is aligned, the shutter 13 is positioned at an angle of 0°.
FIG. 2 shows a high 1-phase sensor signal S1 and a high 2-phase sensor signal S2 when the shutter 13 is positioned within a range of 0°˜30°.
FIG. 3 shows a high 1-phase sensor signal S1 and a low 2-phase sensor signal S2 when the shutter 13 is positioned within a range of 30°˜90°.
FIG. 4 shows a high 1-phase sensor signal S1 and a high 2-phase sensor signal S2 when the shutter 13 is positioned within a range of 90°˜120°.
FIG. 5 shows a low 1-phase sensor signal S1 and a high 2-phase sensor signal S2 when the shutter 13 is positioned within a range of 120°˜180°.
A microprocessor (not shown) generates each sensor signal of each phase and modulates each pulse width of the generated signals, thereby driving the SRM.
FIG. 6 is a curve showing an SRM driving torque in accordance with the conventional art.
As shown, a 1-phase signal having a dwell time of 0°˜120° and 180°˜360° of one cycle of 360°, and a 2-phase signal having a delay of 90° from the 1-phase signal are modulated from the first and second sensor signals shown in FIGS. 2A to 2D thus to be inputted to each winding of the 2-phase SRM. Accordingly, a torque is generated as indicated by the curve of FIG. 3.
However, the conventional art has the following problems. Since the 1-phase sensor initializes and normally-drives a 1-phase and the 2-phase sensor initializes and normally-drives a 2-phase, a sufficient amount of currents are not supplied to each winding of each phase of the SRM at the time of an initial torque occurrence in a normal driving mode (e.g., t1, t2 and t3 of FIG. 3). Accordingly, a torque is not sufficiently generated thus not to normally drive the SRM.
That is, when the 2-phase SRM is driven at a high speed, each phase signal has to be risen at a point prior to an initial point so as to generate a sufficient amount of torque. However, in the conventional art, the 1-phase sensor and the 2-phase sensor detect sensor signals at the same position in an initial driving mode and a normal driving mode, thereby generating each phase signal and a signal for driving the SRM. Accordingly, a sufficient amount of torque is not generated at the time of driving the SRM at a high speed.
Furthermore, a dwell time and a rising delay time of a pulse width modulation signal are controlled based on a phase signal in order to control a rotation speed of the SRM. However, when the SRM is driven at a high speed, the phase signal has a short period and thus the microprocessor has a limited operation speed. Accordingly, it is difficult to control the dwell time and the rising delay time of the pulse width modulation signal based on the phase signal having a short period.